The invention relates to a method and system of delivering energy to material such that the energy is converted to thermal energy in the material and results in a temperature rise which is maximum in a selected region of the material prior to treatment of the selected region to affect therapeutic or other physiological effect.
It is sometimes desirable to cause heat affected changes in a selected portion inside of material, such as living tissue, without causing heat affected changes in portions that lie on either side of the heat affected portion.
Early attempts to use thermal energy to cause useful changes in collagen in attempts to perform thermalkeratoplasty and produce beneficial changes to the curvature of the cornea of the eye relied on heating layers of the cornea. External surface probes were used to apply heat, but resulted in several undesirable problems including epithelial thinning, stromal scarring, necrosis, and lack of reproducibility. Later, microelectrodes were used to apply heat at a set depth and time. Problems of scarring and ulceration were observed. Photothermalkeratoplasty using lasers to apply energy evenly into the stroma without excessive heating of the epithelial layer has been described. Laser energy at wavelengths near 2.6 xcexcm or 3.9 xcexcm were predicted to be efficacious for the procedure. Researchers described a method of cooling the surface layer to affect a beneficial temperature gradient and result in the desired temperature profile after the prescribed application of laser energy.
In 1992 the first use of a pulsed carbon dioxide laser for resurfacing of skin was reported. Skin tightening was discovered as a beneficial side affect of the procedure. The laser was designed to vaporize tissue water by rapid temperature elevation of directly irradiated tissue. The pulse duration was restricted to limit the spread of thermal energy to underlying tissue by conductive heat loss. The thermal profile of tissue after adjacent tissue has been vaporized varies from near 100xc2x0 C. at the surface to near 37xc2x0 C., body temperature, several millimeters below the surface. Desirable treatment of collagen occurs at temperatures near the range of 60xc2x0 C. and 70xc2x0 C. so there is a portion of tissue which reaches this temperature range during laser resurfacing, however, the surface layer or portion reaches temperatures which result in tissue necrosis.
Laser based photoepilation has been the object of study since the advent of the laser. It has been know for several years that optical pulses of the appropriate wavelength, pulse duration, and energy density impinging upon human skin will result in significant and enduring hair loss. The accepted theory for this phenomenon is that the penetration of the laser into the skin and its subsequent scattering results in heating of the hair shafts and follicles through selective absorption by melanin. The absorption of the radiation leads to heating of the follicle and subsequent thermal necrosis.
It has been found that for effective photoepilation to occur the energy must be penetrate approximately 3 mm into the tissue. Prevailing thought indicates that this means the absorption should occur in the melanin and not the oxyhemoglobin, thereby heating the regions around the hair follicle instead of heating the blood and blood vessels. Energy absorption in the melanin leads to elimination of the hair and the reduction or elimination of the ability of follicle to produce hair. Based on the absorption spectrum of melanin and oxyhemoglobin the wavelengths in the neighborhood of 700 nm have been thought to be efficacious. Therefore the Ruby laser at 694 nm, the Alexandrite laser around 760 nm, and flashlamps with emission spectrum centered near 700 nm have been used for this application. The aforementioned lasers are very inefficient, requiring high voltages, large supplies of cooling water. In addition, delivery of the energy to the skin surface is problematic due to the energy required for photoepilation. The pulse energies often exceed damage thresholds of delivery systems or are difficult channel to from the laser to the skin. The flashlamps themselves are inefficient, emit in all directions making efficient energy delivery difficult, and the flashlamps can be cumbersome to use in a handheld device. The convenient and controlled delivery of the optical energy of the appropriate wavelength, fluence and pulse duration to the skin surface for photoepilation in an efficient device has been difficult.
Attempts to cause thermal affected changes in collagen without vaporization or damage to the epithelial layers have met with difficulties. Additionally, most of the method of applying electromagnetic energy to materials such as tissue result in temperature increases which are greater at the surface. Methods to limit the rise in surface temperature by applying lower levels of energy result in heating deeper portions of tissue because a longer time of exposure is required to conduct thermal energy into deeper layers. Methods to minimize surface temperature elevations by using energy sources which have low absorption in the top layer of tissue also result in insufficient or inefficient heating, since these forms of energy generally have lower absorption in the underlying areas also. Attempts to cool the surface in order to limit the temperature rise at the surface, however, result in an increased energy requirement for subsurface heating, which must overcome the incidental subsurface cooling.
Attempts to treat specifically targeted regions within tissue, such as vascular tissue or melanin-containing tissue surrounding hair follicles, have resulted in undesirable temperature elevation in the tissue surrounding the targeted tissue. Utilization of cooling devices, passive as well as dynamic, have been effective in removing heat from surface tissue as well as the tissue surrounding the targeted tissue. However, the subsequent or simultaneous therapeutic treatment to be performed on the target tissue requires delivery of additional energy due to the inevitable cooling of the targeted tissue by the cooling device. The resulting net increase in treatment energy required, therefore, may not only interfere with the efficacy of the cooling device utilized but may also place a greater demand on the treatment energy source.
It is therefore an advantage of this invention to provide an improved system for creating selective temperature profiles in material such as tissue.
It is a further advantage of this invention to provide such a system which utilizes energy with an efficacious absorption coefficient in tissue.
It is a further advantage of this invention to provide such a system which selectively preheats a subsurface region within the tissue to be therapeutically or otherwise physiologically treated.
It is a further advantage of this invention to reduce the level of pulsed energy needed for treatment of the target portions of tissue by preheating the target portions of tissue.
It is a further advantage of this invention to provide such a system which selectively heats a subsurface layer in tissue to cause thermal affected changes in underlying layers of tissue.
It is a further advantage of this invention to provide such a system which selectively heats a subsurface region in skin tissue to cause thermal affected changes in selected regions of the skin without significant heat damage to surrounding regions.
It is a further advantage of this invention to provide such a system which selectively heats a subsurface region in tissue to cause a temperature profile which results in thermal affected changes in the selected region without undesirable thermal affected changes in portions surrounding the selected region.
It is a further advantage of this invention to provide such a system which selectively heats a subsurface portion in tissue to cause collagen shrinkage or collagen regeneration in skin.
It is a further advantage of this invention to provide such a system which selectively heats a subsurface region of vascular tissue.
It is a further advantage of this invention to provide such a system which selectively heats a subsurface region of tissue which contains portions of hair follicles.
In the preferred embodiments, the system for generating treatment energy contains a pulsed energy source, such as a solid-state laser, a neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser, a gas discharge flashlamp, a filament lamp, or an electrical current source.
In a preferred embodiment, energy from the system may be provided through a delivery device, such as but not limited to an optical fiber or fiber bundle or articulated arm for transmitting the light energy to tissue, or a electrically conductive applicator for delivering electrical energy to tissue.
The pulsed energy may be focused on tissue with a focusing lens or system of lenses.
The tissue may be preheated with any operative heating device such as, but not limited to, any intense light source, a gas discharge or other flashlamp, a filament or other incandescent lamp, a laser diode or other laser source, electrical current, probe or conductor, radiofrequency waves, microwaves, ultrasound or other source of electromagnetic energy which penetrates into regions of tissue, by conduction or convection as with a forced air blower, contact device, active or passive heating means, etc., beneath the surface such that the preheating occurs simultaneously with or just prior to the pulsed treatment application of energy from the energy delivery device, thus preferentially preheating a region of tissue without excessive or otherwise undesirable heating of or effect on surrounding tissue.
Material preheating may be accompanied by, at any time either prior to, concurrently with or subsequent to surface cooling, which may be accomplished using either passive or active heat sink or cooling means, to elevate the material forming the selected region or regions to temperatures closer to but yet below the temperature level threshold at which therapeutic or other physiological effect occur.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.